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July 24th, 2000

Messy young massive stars: dust in AFGL 4029

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Messy young massive stars: dust in AFGL 4029

Credit: P. O. Lagage1 & A. Zavagno2
1 Service d'Astrophysique, CEA, FRANCE
2 Observatoire de Marseille, France

(Published in: Zavagno A. et al. 1999, Astronomy & Astrophysics, Vol. 344, p. 499)

Stars in their young age are pretty messy. They spend the beginning of their lives enshrouded in thick clouds of dust, rendering them invisible to the naked eye. Young massive stars in particular sometimes emit large amount of radiation at infrared wavelengths, believed to arise from hot dust grains in their immediate vicinity. However, the exact origin of this emission is still unknown. Infrared cameras allow to peer at their dusty environment, which may constitute the building blocks from which future planetesimals will form.

AFGL 4029 is a luminous bipolar outflow source associated with a young embedded cluster of massive stars, located 2.2 kpc from the sun. We show the image obtained at CFHT with the mid-infrared camera CAMIRAS (Right) compared with the one from the infrared camera on board of ISO, the european infrared satellite (Left). The unprecedented high spatial resolution provided by the CFHT image allows to study in details the morphology of the emission, thus providing information on the nature of the dust as well as the process by which it is heated.

Mid-infrared emission arises from hot dust grains primarily heated by the strong UV field of the close young massive stars. The mid-infrared emission in AFGL 4029 is clearly dominated by two strong sources: IRS 1 (on the right of the image) is a young star still deeply enshrouded in dust (more than 30 magnitudes of extinction in the visible!) and the likely source of the outflow, IRS 2 (to the left) is a B1 star which ionizes its surrounding, creating around it a bubble of hot matter. The mid-infrared emission is clearly resolved spatially in both sources. The extended circular emission observed around IRS 2 coincides remarkably with the known extent of the ionized bubble around the central exciting star. These observations also indicate the presence of a large tenuous enveloppe of small dust particles surrounding IRS 1, most likely a cavity evacuated by the outflow. The arc-shaped nebula to the right of IRS 1 is a reflection nebula. Its strong brightness suggests that it is enriched in small particles, maybe originating in shocks along the outflow.

Technical description:

This image was obtained with the CAMIRAS instrument, a camera working in the mid-infrared (10 to 20 microns). CAMIRAS is a visitor instrument built by the CEA -Saclay (FRANCE) and operated at the CFHT. The pixel size is 0.3" and field of view 57"x38". The image presented here was taken on July 1996 through narrow-band filters ranging from 8 to 12 microns, sensitive both to the continuum emission from the dust and to the infrared emission bands characteristic of small carboneous dust grains.

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